A pizza is cut into slices that are each $\dfrac16$ of the whole. John is going to eat $\dfrac12$ of the whole pizza. How many slices will John eat?
Solution: We can think about this problem like this: $ {\text{number of slices}} = {\text{how much pizza he will eat}} \div {\text{size of each slice}}$ ${\text{?}} = {\dfrac12 \text{pizza}} \div {\dfrac{1}{6} \text{pizza}}$ $\phantom{?} = {\dfrac12} \times \dfrac{6}{1} ~~~~~~~{\text{Rewrite dividing by} {\dfrac{1}{6}} \text{ as multiplying by} \dfrac{6}{1}}$ $\phantom{?} =\dfrac{1 \times 6}{2 \times 1}$ $\phantom{?} =\dfrac{6}{2}$ $\phantom{?} = {3 \text{ slices}}$ He will eat $3$ slices.